CONSERVATIONISTS are looking for farmers to help save a threatened group of rare freshwater pearl mussels.

The invertebrates are becoming scarce and most former populations in England and Wales are almost extinct.

In the North-East and North Yorkshire, examples have been recorded in parts of the Tyne catchment and the upper section of the River Esk, in the North York Moors.

A study of the Esk in 1999 found about 200 of the mussels were living in the river, but all were large adults aged more than 40 to 50 years.

Experts say the lack of young specimens suggests that breeding has not taken place for about 50 years and fear that the Esk population will become extinct in half that time unless action is taken.

The North York Moors National Park Authority is now putting together a funding bid for a project to encourage breeding.

Officials are looking for a farm in the river's upper section where environmental work could be carried out.

Fraser Hugill, the authority's farm conservation officer, said one of the main reasons behind the decline of the pearl mussel was sedimentation.

"As part of the bid, we would like to identify a farm on which to demonstrate good environmental practice which will benefit the pearl mussel and the general ecology of the river," said Mr Hugill.

"This may include fencing off and stabilising river banks, establishing buffers and making stock watering points.

"Ideally, we need a working farm upstream of Glaisdale that has the potential to demonstrate good practice to other farmers or interested groups of people.

"It is a good opportunity for the farmer involved to undertake work that will benefit their farm business."

The freshwater pearl mussel can live for more than 100 years, making it one of the longest-lived invertebrates.

The East Coast populations are thought to be important because their origins are believed to be associated with a time when the rivers on the coast formed part of the European Rhine system.

The populations are thought to be genetically distinct from the majority of the UK populations.

Any interested farms are asked to contact Mr Hugill by Thursday, May 17.